Addition of Halogens to Alkenes

Halogens (bromine and chlorine) add to the double bond to give vecinal dihalides. This reaction takes place at room temperature in a variety of solvents, acetic acid, carbon tetrachloride, chloroform, dichloromethane.


Step 1. Addition the bromine to alkene with form a bromonium ion
Step 2. Nucleophilic attack of bromide anion to the bromonium ion.
Alkenes halogenation is anti reaction.  Bromonium ion can be attacked by bromide ion only from the side opposite the C-Br bond.
Bromination of cyclohexene
Bromination of 1-Methylcyclohexene
Nucleophilic attack by bromide ion take place to more sustituyed carbon in bromonium ion.